1. Field of the Invention
The present invention relates, generally, to a device for detecting the position of terminals of components, and for testing the coplanarity and separation of the same. More specifically, the present invention relates to a device which can detect the position, the coplanarity and the separation of such terminals without overradiating the detector device used.
2. Description of the Prior Art
In the automatic insertion of printed circuit boards, or ceramic substrates, with SMD components (SMD =Surface Mounted Device), the individual components are first removed from a magazine or delivery means using an insertion head and then positioned in a prescribed position on the printed circuit board or ceramic substrate. Since the components have a positional tolerance of approximately 1 millimeter in the magazine or the pick-up position of a delivery device, yet require highly exact positioning on the printed circuit board or ceramic substrate, an automatic position detection and correction method is necessary. Furthermore, the separation and the coplanarity, i.e., the uniform height position of the terminals, must be checked, particularly with SMD components having a large number of poles. Such a check is also performed in the manufacture of the SMD components as part of quality control, for example.
Known methods for position detection and separation checking of the terminals of components typically include the steps of forming an image of the component, or pieces of the component, on a planar CCD camera and detecting both the position and separation of the terminals using digital image processing. However, direct reflections can cause overradiation of the CCD camera wherein resolution is reduced.
U.S. Pat. No. 5,440,391 teaches a triangulation method for measuring coplanarity wherein the height position of a terminal of an SMD component is determined through an illumination of the terminal with light from two directions and a subsequent detection of the two resulting shadows of the terminals with CCD cameras. In an image evaluation unit which is connected downstream to the cameras, the height position of the terminals is determined. Given an impermissible deviation of the coplanarity which would preclude the yielding of a contact by all terminals when the latter are placed on the printed circuit board, the faulty component can be identified and removed from the insertion process. Of course, this method is not suited to checking terminals which are not illuminated by light; e.g., terminals which are located under the component and are shaded from light as such.
A further method is known which uses the diffuse reflection of light at the terminals, instead of using the throwing of shadows, to determine the coplanarity and the separation of the terminals. The terminals are therein illuminated with vertically incident light and their images are formed on a topically resolving detector means through an optical imaging means. The imaging beam path therein forms an angle with the vertically incident light, wherein the angle is not equal to zero degrees, so that the height position of the terminals can be determined by triangulation. In this fashion, the influence of light beams reflected directly into the detector means may be decreased. A modified height position of the terminals therein affects a modified imaging location in the detector means, which location is recognized by an image evaluation means connected downstream. Through a scanning motion along the terminal rows of the component, it can be assured that all terminals are imaged. Because of the different surface nature of the terminals, besides the diffuse reflections, direct reflections of greater intensity reach the detector means causing it to be partially overradiated. Direct reflections occurring far from the actual center of radiation can also reduce the lateral resolution of the detector means. As a result of both effects, the terminal intervals for the separation test are no longer reliably detected.